1. Field of the Invention
The present invention relates to an expansion valve combined with a solenoid valve which is installed in a piping in a refrigeration cycle.
2. Description of the Prior Art
In the conventional refrigeration cycle, an expansion valve is paired with an evaporator and the flow of refrigerant is automatically controlled according to the refrigerating load of the evaporator.
The refrigeration cycle often employs a plurality of evaporators, as in multiple air conditioners and a multistage showcase of a freezer. In this case, because supplying a refrigerant to an evaporator not used is a waste of energy, the flow of refrigerant of liquid phase is stopped by a solenoid valve provided to the evaporator (Japanese Patent Preliminary Publication No. Showa 62-41481).
In a construction where a solenoid valve and an expansion valve are connected together, when the solenoid valve is opened to start the evaporator that was stopped, the refrigerant strikes violently against the inlet of the expansion valve, generating noise and causing a hunting phenomenon in which the expansion valve opens and closes repetitively at short intervals. The impact wave caused by the refrigerant becomes more violent as the amount of refrigerant flowing in increases according to the diameter of the solenoid valve, and its magnitude becomes larger as the capacity of the passage in the solenoid valve and the expansion valve increases. Thus, there is a growing possibility of the expansion valve and the piping being damaged. When the solenoid valve is closed, the flow of the liquid refrigerant is stopped suddenly, causing impact noise by water hammer.
To deal with this problem, the solenoid valve is provided downstream of the expansion valve. This construction has been found to have the following advantages. When the solenoid valve is opened, because there is no throttled portion downstream of the solenoid valve, an impact noise is not produced. When the solenoid valve is closed, the impact noise that is produced at time of closure of the solenoid valve is substantially reduced as the refrigerant throttled by the expansion valve located upstream of the solenoid valve is gasified.